a. Field of the Invention
The instant invention relates generally to catheters and to introducer catheters used to help deliver catheters or other medical devices to locations within the human body. In particular, the instant invention relates to catheters and introducer catheters having a torque transfer layer configured to provide increased strength, flexibility, and kink resistance.
b. Background Art
Catheters are used for an ever growing number of medical procedures. To name just a few examples, catheters are used for diagnostic, therapeutic, and ablative procedures. Typically, the physician manipulates the catheter through the patient's vasculature to the intended site, such as a site within the patient's heart. The catheter typically carries one or more electrodes or other diagnostic or therapeutic devices, which may be used for ablation, diagnosis, cardiac mapping, or the like.
It is known that, to facilitate placement of the diagnostic or therapeutic catheter at a location of interest within the patient, it may be introduced through another catheter, commonly known as a “guiding catheter” or “introducer catheter,” and the terms will be used interchangeably herein. Generally speaking, an introducer catheter is a tube having a high degree of directional control that is used to place other catheters, which may have little or no directional control, into specific areas of the patient's body.
In the field of cardiac ablation, for example, introducer catheters may be used to negotiate the patient's vasculature such that an ablation device may be passed therethrough and positioned to ablate arrhythmia-causing cardiac tissue. The introducer catheter itself may be advanced over a guide wire.
Generally, it is known that the introducer catheter must have an overall diameter small enough to negotiate blood vessels while retaining an inner diameter (or “bore size”) large enough to accommodate the ablation device therethrough. Furthermore, since the path within the patient is often long and tortuous, steering forces must be transmitted over relatively great distances. Accordingly, it is desirable for the introducer catheter to have sufficient axial strength to be pushed through the patient's vasculature via a force applied at its proximal end (“pushability”). It is also desirable for the introducer catheter to transmit a torque applied at the proximal end to the distal end (“torqueability”). An introducer catheter should also have sufficient flexibility to substantially conform to the patient's vasculature and yet resist kinking as it does so. One of ordinary skill in the art will recognize that these various characteristics are often in tension with one another, with improvements in one requiring compromises in others. For example, increasing the bore size of an introducer catheter having a given overall diameter requires utilizing a thinner wall. A thin-walled introducer, however, is more likely to collapse upon itself when a torque is applied at its proximal end.
To improve pushability, torqueability, flexibility, and kink resistance, many extant introducer catheters utilize one or more reinforcing layers in their construction. For example, the guiding catheter disclosed in U.S. Pat. No. 4,817,613 to Jaraczewski et al. (“Jaraczewski”) includes a pair of braided torque transmitting layers sandwiched between a flexible tubular member and a flexible plastic casing applied as a viscous material and subsequently cured. Jaraczewski also teaches, however, that to a certain degree, flexibility comes at the expense of torqueability. Further, depending on the thickness of the torque transfer layers, they may increase the wall thickness, thereby either increasing the overall diameter of the introducer catheter for a given bore size or decreasing the bore size for a given overall diameter.
Many extant large bore introducers (i.e., an introducer catheter with bore size of greater than about 6 French), in order to find a suitable balance of pushability, torqueability, flexibility, and kink resistance, have outer layers that are relatively stiff, which compromises torqueability, kink resistance, and flexibility for pushability.